Previously, as a member for reinforcing a shape of a fiber sheet, a separator having a corrugated shape or the like has been devised in JP-A No. 4-290997 and JP-A No. 2002-336629, and a wrought fiber sheet with a comb-like separating material inserted therein has been devised in JP-A No. 9-173748. However, since as a separating material used in the previous configuration reinforcing member, a metal such as aluminum and the like, and olefin-based, polyamide-based, synthetic rubber-based and urethane-based resins are used, and since these reinforcing members are not biodegradable, there was a problem in that, even when a fiber sheet part is degraded, a reinforcing member is hardly degraded. Further, a method for crosslinking-fixing a hot melt resin at an apex of a pleat shape has been devised in JP-A No. 64-63012 gazette. However, the method had a problem in that the hot melt resin is a resin such as copolymerized polyamide, ethylene-vinyl acetate copolymer, polyolefin or the like, and is not biodegradable like the aforementioned separating material.
Similarly, as a frame member for accommodating a wrought fiber sheet, a non-combustible material, for example, a metal such as aluminum and the like, and olefin-based, polyamide-based, synthetic rubber-based, and urethane-based resins are used. Since these frame materials are not biodegradable, there was a problem in that, even when a wrought fiber sheet is degraded, a frame material is hardly degraded.